Experiments have been designed to explore the possibility of specific chromosomal arragements in nuclei. Colchicine has been demonstrated to reduce the amount of somatic crossing over occurring in interphase nuclei in soybeans. Other studies in progress on somatic crossing over include a further definition of the biological parameters of the soybean test system and the synthesis of a stock carrying both an asynaptic gene and genes necessary to detect somatic crossing over, so that the effect of a meiotic mutant on somatic crossing over can be ascertained. A specific arrangement of nonhomologous chromosomes has been observed in the haploid generative nuclei of Ornathogalum virens. An "Asynaptic" bivalent has been observed in pachytene spermatocytes of the sand rat Psammomys obesus. Sunaptic failure appears to be due to a large pericentric inversion. When asynaptic, the ends of the bivalent both self-associate and associate with the ends of the unpaired sex chromosomes. In late pachytene nonhomologous synapsis occurs and the bivalent now lies on the opposite side of the nucleus from the sex chromosomes. This and other evidence suggests an active role of chromosome ends in homologous recognition. Other work in progress includes examination of mitotic nuclei for exidence of specific chromosomal arrangements and for an indication of how this order may be maintained.